1. Field of the Invention
This invention relates to the production of butanediol, and, more particularly, to a process of producing a distilled butanediol product of high quality in high yield.
2. Description of the Prior Art
Butanediol is prepared by catalytic hydrogenation of butynediol, as described in U.S. Pat. No. 3,449,445. The butynediol is obtained by a catalytic ethynylation reaction between aqueous formaldehyde and acetylene, which is described, for example, in U.S. Pat. Nos. 2,871,273, 2,939,844, 3,108,140, 3,294,849, 3,560,576, 3,723,545 and 3,920,759.
The butynediol solutions that are produced by ethynylation, however, contain a number of impurities, including dissolved salts, such as sodium formate, calcium formate, magnesium formate and sodium acetate; silicic acids and silicic acid salts, and some unreacted formaldehyde. These impurities arise in a variety of ways. The formates always are present as a result of the Canizzaro reaction of the formaldehyde reactant with itself. Sodium acetate results when it is used as a buffer to control the pH of the reaction medium during ethynylation. Calcium and magnesium ions, and silicic acids and silicic acid salts, are leached out of the ethylation catalyst.
These aforementioned salts, particularly the formates and acetates, interfere with the final distillation step of producing the butanediol product, and the other impurities, such as the metallic ions, the silicic acids and silicic acid salts, and the excess formaldehyde, reduce the lifetime of the hydrogenation catalyst used to convert the butynediol to butanediol.
In particular, it has been found now that during this final fractional distillation of the butanediol product from the crude butanediol solution, the residue of the distillation forms a gel, even at high temperatures, thus trapping part of the butanediol and reducing the yield thereof. This highly undesirable result is compounded by the fact that the gelled residue containing butanediol does not flow and cannot be pumped. Accordingly, it has been necessary, in the past, whether in a batch or continuous process, to leave a considerable amount of butanediol liquid with the gelled residue to keep it fluid and pumpable, thus contributing further to loss of yield of product. In actual plant operation, at least 5% of the butanediol liquid must be left in the residue to insure a fluid condition.
Prior to this invention, there was no satisfactory means by which to resolve the problems of loss of yield by gel formation, and loss of activity and lifetime of the hydrogenation catalyst.